A problem with very late game nuclear setups is that they cannot be scaled indefinitely because of radiation.

Even if you try to reduce radiation as much as possible some radiation producing waste is still on the belts or at reprocessing plants etc.
The only way to scale nuclear up further is to just build fast breeders and no other reactors which is a bit sad in my opinion.

A simple fix to this problem would be to introduce a repeatable research which increases the radiation resistance. Each level of this research could increase the amount of radiation which doesn't incur any penalties and could in addition reduce these penalties.